The invention relates to rotary actuator systems for optical heads for optical disk drive systems, for example, compact disk read only memories (CD ROMS) and magneto-optical disks.
Emerging optical read and write disk drive technologies promise greatly improved storage densities. However, existing magnetic disk drive technologies have established access speed standards which will be difficult to meet. Existing write once and read only disk drives have seek times much longer than their magnetic counterparts. The higher density of optical disks results primarily in more closely spaced data tracks with tracking tolerances tighter by an order of magnitude. Thus, in order to realize their potential competitive advantage, optical drives must meet already challenging seek time specifications while being even more precise.
An optical disk can have either many tracks in the form of concentric rings or one long spiral track. With concentric tracks, the track pitch is the distance along a radius from one track to the next. For a spiral, the pitch is the radial distance the read head moves when following the spiral for one revolution of the disk. Track pitch for optical drives is about 1 micron, as determined by the diffraction-limited spot size of an 820 nanometer diode laser.
Optical disk drives require a movable optical head positioned by an actuator. The purpose of the head positioning actuator is to seek from one track to another. The total radial excursion of the optical head necessary to cover the data area of the disk is called the stroke.
There are two distinct types of head actuators for optical disk drives: rotary and linear. In a rotary head actuator, the body of the actuator pivots on rotary bearings and the head sweeps out an arcuate path. A linear actuator translates along a single axis radially relative to the disk axis.